The present invention relates in general to measurement of heat flux in different furnace locations and more particularly to an attachable heat flux meter using thermocouples.
The measurement of the heat absorbed by a furnace wall can be calculated by knowing the difference between the temperatures of two points that are parallel to the flow of heat through a material that separates the heating source from the cooling source. In large steam generating boilers, the combustion of the fuel inside the furnace creates combustion gases and ash particles that radiate energy to the enclosure walls of the furnace. The enclosure walls consist of pressurized water cooled tubes that are connected with metal bars, referred to as membrane or webs, and which provide a gas tight barrier that keeps the high temperature furnace gases inside the enclosure. The radiant heat from the combustion gases inside the furnace are absorbed by the furnace walls and the rate at which the heat is absorbed by unit area is referred to as heat flux.
Many different known concepts are used to determine the heat flux absorbed in a location of a furnace. Calorimeter, Gardon gage, heat pipes and various thermocouple types of heat flux probes are used and they vary in cost and effectiveness.
One known chordal heat flux measurement device is manufactured by The Babcock and Wilcox Company. This type of measurement device requires drilling at least two openings along the surface of a boiler tube and installing a thermocouple into each of the openings. The ends of the thermocouples are located at the crown of the tube (the closest point along the curvature of the tube that heat can be absorbed on the inside of the furnace wall) at an acceptable distance apart. Using the temperature readings from the thermocouples and knowing the distance that the thermocouples are apart provides data that are used in calculating the heat flux of the energy absorbed by the tube. In most applications, an additional thermocouple is attached to the unheated side of the tube so as to measure the temperature of the fluid flowing through the tube. A brochure that describes a SDF type of chordal thermocouple is entitled xe2x80x9cChordal Thermocouplesxe2x80x9d and is available from The Babcock and Wilcox Company.
Another heat flux meter called the Fluxdome is marketed by Land Combustion Inc. This device is used for boiler applications to measure the heat flux at a point on a tube, and consists of thermocouples that are placed into a metallic cylinder that is welded on the crown of the furnace tube. The heat flux is determined from the measured temperature difference between the two thermocouples, knowing the distance between the couples and the thermal conductivity of the material in which the thermocouples are embedded.
All such known devices require the placement of thermocouples or other measuring devices on the furnace tubes by drilling into the tube. This is undesirable and dangerous since it weakens the tube wall. A device is thus needed that will not require entering the furnace enclosure or the weakening of the furnace tube walls.
The present invention solves the previously mentioned problems associated with prior art devices by attaching a heat flux device to the boiler tube membrane. The concept of this invention is to measure the heat flux at the membrane location of the furnace wall. The attachable heat flux meter is inserted into an opening that is drilled into the center of the membrane between two tubes of the furnace wall. This opening is drilled through the membrane and is sized slightly larger than the diameter of the metal cylinder of the heat flux device. The device allows the heat absorbed on the surface of the metal cylinder to flow down the cylinder and into the membrane of the furnace wall. The heat flux meter is attached to the outside or casing side of the furnace by welding the bracket of the device to the membrane.
The measurement of the heat flux is determined in a similar fashion as the chordal thermocouple. Two thermocouples are installed in the meter at a set distance apart. The heat flux is calculated through known heat conduction equations. By knowing the temperatures from the two thermocouples, the vertical distance between the two thermocouples, and the conductivity of the material in which the thermocouples are imbedded, the heat flux at the membrane location can be calculated by a known equation.
In view of the foregoing it will be seen that one aspect of the present invention is to provide a heat flux measurement device that does not require penetration of pressure parts such as the furnace wall tubes.
Another aspect of the present invention is to provide a heat flux measurement device that is easily installed from the outside or casing side of the furnace.
These and other aspects of the present invention will be more fully understood from a review of the following description of the preferred embodiment when considered with the accompanying drawings.